Magnetic refrigeration technology at ambient temperature has been known for more than twenty years and its advantages in terms of ecology and sustainable development are widely acknowledged. Its limits in terms of its useful calorific output and its thermal performance are also well known. Consequently, all the research undertaken in this field tends to improve the performances of the magnetocaloric thermal appliances, by adjusting the various parameters, such as the intensity of the magnetic field, the performances of the magnetocaloric material, the heat exchange surface between the heat transfer fluid and the magnetocaloric materials, the performances of the heat exchangers, etc.
In these appliances, it is indispensable to generate a uniform and intense magnetic field in at least one air gap wherein at least one element out of magnetocaloric material is placed and removed. The higher the magnetic field, the stronger the magnetocaloric effect of the element out of magnetocaloric material, which leads to an increase in thermal output and therefore in efficiency of a magnetocaloric thermal appliance.
Moreover, in certain areas, the compactness of the thermal appliance is essential and leads to a rotary configuration or structure wherein the magnetic system is in relative movement with respect to the magnetocaloric material(s). Such a rotary configuration has the advantage of showing a good magnetocaloric material per used volume ratio. Since the thermal output of the thermal appliance depends in particular on the quantity of magnetocaloric material used, such arrangement is actually very advantageous.
Publications WO 2005/074608 A2 and US 2005/0046533 A1 describe a magnetic field generator as defined in the preamble of claim 1, comprising in particular two diametrically opposite air gaps wherein a magnetic flux circulates in the same direction but belongs to two distinct magnetic loops, the return of the magnetic loops taking place through the central axis of the generator, which corresponds to the rotary axis of said generator.
Now, this central axis made out of a magnetically permeable material must be thick enough, and therefore show enough material, to allow conducting the magnetic induction flux of the two magnetic loops without leading to magnetic saturation. This generator type therefore has a major drawback that consists in its high weight which on the one hand makes it difficult to handle and, on the other hand increases accordingly the weight of the magnetocaloric thermal appliance it is integrated in.
For this reason, there is today no magnetic generator with a reduced size, a limited weight, low manufacturing costs, that can be mounted in a rotary appliance and is able to generate a magnetic field of at least one tesla.